class Solution {
public:
    int change(int amount, vector<int>& coins)
    {
        int n = coins.size();
        vector<int> dp(amount + 1, 0);
        dp[0] = 1;
        for (int i = 1; i <= n; i++)
        {
            for (int j = coins[i - 1]; j <= amount; j++)
            {
                dp[j] += dp[j - coins[i - 1]];
            }
        }
        return dp[amount];
    }
};